New and improved technologies are needed for monitoring perchlorate contamination in groundwater. TDA Research Inc. proposes a new portable sensor platform for in-the-field monitoring of the perchlorate anion, ClO4-, for which the recommended remediation goal is less than 3.6 parts-per-billion (3.6 ppb) in water. Perchlorate is a toxic anion that interferes with the uptake of iodide (a necessary element in thyroid hormones) by the thyroid. This inhibition decreases the production of thyroid hormones; thus, exposure to perchlorate needs to be avoided by the developing fetus as well as by infants and children. Perchlorate is highly water soluble, stable, and difficult to detect by chemical or instrumental means. It can be transported by groundwater over long distances, leading to extensive and persistent contamination. Both drinking water sources and food supplies can be contaminated by perchlorate. Therefore, detecting and quantifying perchlorate is a priority for safety and for remediation efforts. On-site, portable methods for quantifying and remote monitoring of perchlorate in the field are particularly sought to reduce the number of laboratory analyses, reduce costs and facilitate the automated acquisition and communication of real-time concentration data. Monitoring such low levels of perchlorate is difficult even in the laboratory, and is especially hard in the field, where a rugged analyzer is needed for unattended operation. In this project we will provide an improved method for the analytical quantification of perchlorate in water by combining new perchlorate-specific chemosensors with advances in spectrofluorimetry equipment. In Phase I we will synthesize a new chemosensor probe, validate its sensitivity (the ClO4- detection limit in parts-per-billion (ppb), with a goal of high parts-pe-trillion (ppt) accuracy) and selectivity (specificity for ClO4- in the presence of other anions), ad demonstrate its utility with field-portable instrumentation. In Phase II and later project phases w will develop an integrated device for the real-time on-site remote quantification of ClO4- in water samples. The sensor platform will be rapid, portable and computer-controlled, for ready interface with other types of groundwater probes and compatible with computer network data communication. The commercial products created in this work will support the identification, monitoring and cleanup of water at sites contaminated with perchlorate.